This program will bring experimental techniques, biological systems, demographic concepts, statistical methods, and theoretical models to bear on questions concerning the determinants of life span in both humans and in non-human model systems including both vertebrates (comparative demography of mammals; birds) and invertebrates (fruit flies; nematodes; honey bees). The five research projects that form the program are organized around the following crosscutting themes: (1) Life span is adaptive and shaped by nature; (2) Individuals age in the wild; (3) Sociality and life span are mutually affecting; and (4) Superarching principles provide all embracing order to variation in animal life spans. The program will generate new large-scale demographic databases for the honey bee, wild medflies, and C. elegans and life history data from the literature on several dozen vertebrate species, introduce new statistical models for analysis of demographic data on model species, develop a novel methodology for studying aging in the wild, develop more fully the mathematical foundations of biodemography, generate new models and theories concerned with the role of intergenerational transfer and sociality in the evolution of life span, explore questions concerned with the effects of stochastic environments on the evolution life span and hazard rates, and use comparative demography to identify general principles concerning life span evolution.